| Summary: | The ocean takes up 93 % of the excess heat in the climate system and approximately a quarter of the anthropogenic carbon via air-sea fluxes. Ocean ventilation and subduction are key processes regulating the transport of water from the mixed layer to the ocean's interior, which is isolated from the atmosphere for a timescale set by the large-scale circulation. Using numerical simulations, we assess where the ocean subducts water and takes up properties from the atmosphere, and how ocean currents transport and redistribute these properties. A set of passive tracers are released annually from different ocean surface “patches”, representing water masses’ source regions. We show that interannual variability in subduction rates, driven by changes in surface forcing, is key in setting the different sizes of the long-term inventory of the dyes. Both hemispheres exhibit a strong correlation between the strength of ventilation in recently subducted waters and the longer-term dye inventory. This means that the conditions close to the time of dye injection are driving the amount of seawater being subducted, but also that this signal persists over time and the longer-term tracer inventory is strongly related to the initial surface conditions. The correlation is even stronger for the different source regions. Export and isolation of subducted waters is faster in the Northern Hemisphere, defining a stronger ventilation “persistence, represented by the slope of the correlation between subduction and the longer-term inventory. The highest ventilation persistence is found in the subpolar North Atlantic, dominating tracer’s retention on multi-decadal time scales.
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